Technical Abstract:
Water-soluble anionic polyacrylamide (PAM), a nontoxic polymer, controls soil erosion and increases infiltration in irrigation furrows. We hypothesized that post-irrigation deep percolation and preferential- flow patterns for the PAM-treated and conventionally irrigated (CI) furrows would differ. Portneuf silt loam plots 179 m long were planted to corn. For PAM furrows, we added polymer to advancing irrigation furrow streams at 10 ppm. Inflow rates during furrow advance were 3X greater than that of untreated CI furrows. Vacuum assisted percolation samplers at 1.2 m depth were used to monitor daily soil water flux and nitrate-N and Cl concentrations. Under CI, percolation rate started high the first day after irrigation, declined during the second and third days to a value about half that of the first day, then rose to a second peak between 6 and 7 days after irrigation. PAM percolation rate started low on the first day after irrigation, peaked at about twice the initial rate on day two or three, declined through day four or five, then rose to a second peak between 6 and 8 days after irrigation. Water moved rapidly downward from CI furrows after irrigation, and included bypass flow that diluted nitrate concentrations in deep percolation water.